A stressful pregnancy matters — it can affect a baby’s genes

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Everyone has heard of postnatal depression, but not everyone knows that mothers are as likely to be depressed during pregnancy as afterwards. As well as the distress of the mother herself, this matters because of the effects on the developing baby in her womb. We have long known that how we turn out depends on how our genes interact with our environment. We now know the environment starts before birth. How we develop there can affect our health and wellbeing for the rest of our lives. If we are born too small, for example, we are more likely to have cardiovascular disease later.

Many pregnant women are anxious or depressed, and this can affect how the baby’s brain develops. This in turn leaves the child at greater risk of anxiety, depression, slow learning or behavioural problems such as ADHD later. If the pregnant woman is in the top 15 per cent of the population for symptoms of anxiety or depression this doubles the risk of her child having emotional or behavioural problems. The risk of the child at 13 years old having a mental health problem goes from about 6 per cent to 12 per cent. (This is on top of the influence of other factors such as the mother’s smoking, alcohol consumption, poverty, educational level, and her emotional state after birth.)

Research has shown the effects of a range of different types of stress on the pregnant woman, as well as anxiety and depression. If she was exposed to great stress, such as being in Manhattan during 9/11 or in a freezing ice storm in Canada, this could have an impact on her baby’s developing brain. Relationships, especially with the father, matter too. A supportive partner can buffer against these effects, but an unsupportive or abusive one can stress the mother in a way that harms her developing baby.

How the baby develops in the womb then can thus set the trajectory for later. This is foetal programming. Calling this ‘programming’ does not mean it is irreversible. The care of the newborn baby is just as important, and the later environment matters too. The quality and sensitivity of the care after birth can boost or dampen the effects of the programming before birth. The brain remains open to change to some extent throughout life. But it is especially so at the beginning. The brain increases 16-fold in size during the second half of gestation and the neural pathways are starting to be formed — how this occurs can be changed by the chemical signals received from the mother’s blood.

Children can be affected in different ways by the mother’s stress during pregnancy, and most are not affected at all. In what ways and how far each child is affected depends partly on his or her genetic make-up. There is not a single gene for a problem such as ADHD or depression. There are many variations which each make a small contribution and which interact with the environment, including in the womb.

We are starting to understand how all this happens. We know that the mother’s mood can affect the function of her placenta. If the mother is more anxious there is less of the enzyme that breaks down the stress hormone cortisol, for example; and the development of her baby’s brain can be affected by being exposed to more cortisol. We also know that if the mother is stressed, anxious or depressed while she is pregnant, this can lead to epigenetic changes in her child. These are not changes to the basic sequence of the DNA in each gene, but changes to the control of each gene, how much each is switched on or off. We are just at the beginning of our understanding of all these mechanisms, and many other biological systems are likely to be involved too.

Why should all this be happening? It makes some sense in evolutionary terms. Our ancestors will have felt stressed if there were physical dangers around, such as predators, or hostile neighbouring tribes. The changes we see in the child may have been protective in such an environment. More anxiety means greater vigilance and more ability to detect danger. Readily distracted attention, as in ADHD, may have helped to spot the danger more quickly. Rapid aggression may have helped also. But these changes, adaptive in the presence of real danger, are disadvantages in our society.

The good news is that we should be able to do something about all this. At the moment most anxiety, depression and stress in pregnant women is not detected by health professionals and very little is done to help. Mental health is the most neglected aspect of obstetric care. But it is not difficult either to detect or to help. If we can help the pregnant woman we will be helping the next generation too.

Vivette Glover is professor of perinatal psychobiology at Imperial College London.